I made this hack for my IKEA Alex drawers to make them open up all the way. Originally they leave about 20 cm inaccessible in the back, but with my hack it now continues to slide on the printed rail. You will need to make a hole in the side of the drawer, so continue at your own risk!

You will need to cut a portion of the side of the drawer in the rail notch to fit the printed piece. I did this using a (sharp) Stanley knife and cut along the edges of the notch. I started from the front of the original screw hole, and then backward 16 cm. Probably best to do leave it a bit on the tight side to make sure the printed piece will fit tightly.

You will also need a longer screw than the original. I found some in my box of screws that may come in handy some day that worked nicely. The ones i used are 15mm in length and the diameter is 3.8mm. Make sure not to tighten them to much as it will not slide well. 

I printed the pieces using an A1 Mini (two on one plate) with some white PLA. Takes about 50 minutes to print.

By the way, I'm posting this on my third day 3D printing so I'm still a noob. Feel free to tweak the design or remix this in any way :)

UPDATE: Added a printable hole template that you can place on the drawer to make a hole that fits the insert